Herbivore-induced volatile production by Arabidopsis thaliana leads to attraction of the parasitoid Cotesia rubecula: Chemical, behavioral, and gene-expression analysis

Many plant species defend themselves against herbivorous insects indirectly by producing volatiles in response to herbivory. These volatiles attract c arnivorous enemies of the herbivores. Research on the model plant Arabidops is thaliana (L.) Heynh. has contributed considerably to the unraveling of s ignal transduction pathways involved in direct plant defense mechanisms aga inst pathogens. Here, we demonstrate that Arabidopsis is also a good candid ate for studying signal transduction pathways involved in indirect defense mechanisms by showing that: (1) Adult females of Cotesia rubecula, a specia list parasitic wasp of Pieris rapae caterpillars, are attracted to P. rapae -infested Arabidopsis plants. (2) Arabidopsis infested by P rapae emits vol atiles from several major biosynthetic pathways, including terpenoids and g reen leaf volatiles. The blends from herbivore-infested and artificially da maged plants are similar. However, differences can be found with respect to a few components of the: blend, such as two nitriles and the monoterpene m yrcene, that were produced exclusively by caterpillar-infested plants, and methyl salicylate, that was produced in larger amounts by caterpillar-infes ted plants. (3) Genes from major biosynthetic pathways involved in volatile production are induced by caterpillar feeding! These include AtTPS10, enco ding a terpene synthase involved in myrcene production, AtPAL1, encoding ph enylalanine ammonia-lyase involved in methyl salicylate production, and AtL OX2 and AtHPL, encoding lipoxygenase and hydroperoxide lyase, respectively, both involved in the production of green leaf volatiles. AtMOS, encoding a llene oxide synthase, involved in the production of jasmonic acid, also was induced by herbivory.